1. Field of the Invention
The present invention relates to a liquid crystal display backlight and a liquid crystal display device. More specifically, the present invention relates to a small liquid crystal display backlight having a fine heat dissipative characteristic and to a liquid crystal display device.
2. Description of the Related Art
Conventionally, a cold cathode tube has been mainly used as a backlight light source of a liquid crystal display device. However, in that case, it is necessary to have an exclusive lighting circuit and to deal with a high voltage. Therefore, recently, an LED (light-emitting diode) is used especially for small devices such as a portable telephone and a PDA. The LED provides pseudo white light that is obtained by applying YAG phosphor mainly to a blue LED, and it has a difficulty in terms of color reproducibility (particularly in reds). The LED has not been used often as a monitor and for a TV, because it has only a small amount of light, is more expensive than the cold cathode tube, and has difficulty in terms of the color reproducibility as described above.
However, recently, the efficiency of the LED has been improved dramatically. At the same time, an LED capable of conducting a large electric current has been developed. Associated with the environmental issues and achieving expanded color reproducibility, there has been an active movement to try to produce a relatively large backlight using the LEDs.
A compact lighting system and a display device are known (see Japanese Patent Application Publication 2004-527069 (Patent Document 1), for example) as a lighting unit that uses the liquid crystal display backlight described above. Patent Document 1 discloses a lighting system which uses a plurality of LEDs provided between light-mixing panel parts 151 and 152 which are disposed on a same plane via a spatial area, as in a structure shown in FIG. 12, for example.
That is, the lighting system shown in FIG. 12 includes a light-emitting panel 101 and a pair of mixing panels 151, 152, and LEDs 106 are arranged in two rows as a light source. The LEDs 106 are configured with first and second light-source sections 161 and 162. The light emitted from the first and second light-source sections 161, 162 makes incident on each of the panel parts 151, 152 from each of a first and second light input edge areas 171, 172 of the light-mixing panel parts 151, 152 via respective light collimators 161A, 162A.
The light made incident on the light-mixing panels 151, 152 repeats total reflection within the light-mixing panels 151, 152, and it is emitted from a light output edge areas 181, 182 on the end faces of opposite sides to light transfer chambers 191, 192 to be sent to the light-emitting panel 101 from the respective light output edge areas 181, 182.
Note here that reference numerals in FIG. 12 are numerals obtained by adding “100” to the reference numerals applied in FIG. 3B of Patent Document 1, and the structures thereof are completely the same. Numeral references (161A, 162A) for the light collimators, however, are reference numerals obtained by simply adding A, B to the original numeral references (161, 162) of Patent Document 1.
FIG. 1 and FIG. 2 of SID 2003 DIGEST, pp. 1259-1261 (Non-Patent Document 1) disclose a technique for building an area light source in which: LEDs having a dome-type lens are arranged in an array; output light from the LEDs is guided to a first light guide plate via a reflector (light reflection guide); and the light is sent to a second light guide plate (light-emitting plate) via another reflector.
In the lighting system disclosed in Patent Document 1 described above, the two rows of light-source sections 161, 162 are provided neighboring to each other with the light collimators 161A, 162A for reflecting the light from the light-source sections 161, 162 being in contact with each other.
The two rows of light-source sections 161 and 162 are provided for obtaining intensified brightness by mounting the double LEDs. However, the light-source sections 161 and 162 are very close to each other, so that the durability is deteriorated greatly because of the heat generated from each other, etc. In addition, the brightness thereof cannot simply be doubled. In order to lighten and eliminate the influences of the heat, a heat dissipation device is required.
However, there is no specific disclosure in Patent Document 1 regarding such heat dissipation device. For mounting a heat dissipation structure to the lighting system disclosed in Patent Document 1, it is necessary to provide a required heat dissipation device on the outer side of the two rows of light-source sections 161 and 162. If so, the whole device comes to have increased thickness, scale, and weight, which makes it difficult to thin and lighten the device. Such shortcomings exist also in Non-Patent Document 1 mentioned above.